Floating reservoir cover

ABSTRACT

Floating cover assembly having diaphragm which lies directly on surface of body of liquid. Edges of diaphragm extend beyond edge of liquid and have stiffening members which are resiliently secured by anchoring lines to ground anchors. Resilient anchoring lines or freely hanging weights hold diaphragm in place relative to liquid, and permit diaphragm to move in response to change in liquid level. Thus diaphragm is always supported by liquid, and tension in diaphragm is low.

United States Patent 1191 Collins et a1.

[ June 11, 1974 FLOATING RESERVOIR COVER [76] Inventors: James BensonCollins, 2795 W. 50th Ave., Vancouver, British Columbia; Frank WilliamFarrow, 874 Underhill Dr., Delta, British Columbia, both of Canada 22Filed: Mar. 23, 1973 211 Appl.No.:344,233

52 Us. (:1... 61/1, 4/17212, 220/26 R s1 1 1m, 01.; E02b 865g 5/00 58Fieldot Search 6l/.5, 1, 7; 220/18, 26 R,

220/26 S, 26 D, 26 SA; 4/l72.12', 172.14,

[56] References Cited UNITED STATES PATENTS 3,330,| 18 7/1907 Biais6l/.5 0,501,917

3/1970 Detter 61/1 R 6/1970 Renshaw et a1 61/1 R 6/1972 Dial 220/26 SPrimary Examiner-W. C. Reynolds Assistant Examiner-Philip C. KannanAttorney, Agent, or Firm.-Carver and Company [57] ABSTRACT Floatingcover assembly having diaphragm which lies directly on surface of bodyof liquid. Edges of diaphragm extend beyond edge of liquid and havestiffening members which are resiliently secured by anchoring lines toground anchors. Resilient anchoring lines or freely hanging weights holddiaphragm in place relative to liquid, and permit diaphragm to move inresponse to change in liquid level. Thus diaphragm is always supportedby liquid, and tension in diaphragm is low.

, 16 Claims, 12 Drawing Figures zwimwm 1 1 mm ale-315L367 SHEET 1 OF 4 E/3 E 's 22 22b E 2; E 59 E Hmmmmuumnmumummnu mm.

PATENTEDJUN 1 1 1914 $815,367

SHEET 2 BF 4 FLOATING RESERVOIR coVER BACKGROUND OF THE INVENTION Analternative is to provide a cover floating on the surface of thereservoir. The floating cover has discrete floats secured to a lowersurface thereof, the floats providing bouyancy so that portions of thelower surface of the cover are generally clear of the liquid, thebouyancy being sufficient to sustain loads from rain or snow. Means ofdraining the cover are provided, usually a pump draining afsump. Algaetends togrow on the surface of the water, on the lower surface of thecover, and

' on the floats, which algae can be difficult to remove.

Difficulty associated with such a floating cover includes anchoring theperiphery ofthe cover so that variation in liquid level can beaccommodated by the cover without incurring excessive tension in thecover.

SUMMARY OF THE INVENTION The invention reduces difficulties of the priorart by providing a cover assembly that is supported directly on thesurface of the liquid and additional buoyancy is eliminated, thusfacilitating cleaning. As the cover rests on the'main portion of theliquid surface, air is excluded from the surface and, with an opaquecover to obstruct sunlight, algae growth is inhibited. The body ofliquid to be protected has a periphery. defined by inner faces ofsurrounding containing walls, which inner faces usually slope inwardsand downwards.

One embodiment of the invention has a floating cover assembly having aflexible impermeable diaphragm having upper and lower faces, an edgedefining a periphery thereof, the lower face being adapted to lie on theupper surface of the-liquid, edges of the diaphragm being spacedoutwards from the periphery of the liquid. A'plurality of elongatedstiffening members adjacent the periphery of the diaphragm cooperatewith the diaphragm. Anchoring means secured relative to the containingwalls are spaced outwards from the periphery of the diaphragm, andresiliently tensioned anchoring links extend between the diaphragm andthe anchoring means. The periphery of the diaphragm is thus anchored tothe containing walls and resilience in the anchoring links permits thediaphragm to move in response to a change in liquid level from apredetermined high level to apredetermined low level. Thus the diaphragmis always supported by the liquid, producing relatively low tension inthe diaphragm. A sump is fitted at a lowest position of the diaphragmand drains liquid collected on the upper surface of the diaphragm, drainmeans in the sump removing liquid from the sump.

A detailed description following, related to the drawings, describesembodiments of the invention which is DESCRIPTION OF THE DRAWINGS FIG. 1is a simplified top plan View of a reservoir and reservoir coverassembly according to the invention,

FIG. 2 is a simplified section on 22 of FIG. 1,

FIG. 3 is a fragmented section at enlarged scale on a portion of 22 ofFIG. 1, showing an alternative embodiment of a sump,

FIG. 4 is a simplified fragmented perspective of an edge of the coverassembly and associated containing wall, showing two embodiments ofmeans to secure an edge of the assembly, some portions being removed,

FIG. 5 is a simplified fragmented perspective of a cover showing analternative means of securing an edge of the cover assembly, someportions being removed,

FIG. 6 is a simplified fragmented perspective showing a furtheralternative means of securing an edge of the cover assembly, someportions being removed,

- FIG. 7 is a simplified section through a portion of the containingwall showing one means of supporting a stiffening member associated withan edge of the cover assembly,

FIG. 8 is a simplified fragmented elevation on 8-8 of FIG. 7, someportions beingremoved,

FIG. 9 is an alternative means of supporting stiffening members,

FIG. 10 is a simplified section on l0 l0 of FIG. 9,

FIG. 11 is a simplified fragmented side elevation of a furtheralternative anchoring means and edge of diaphragm, as seen from ll'll ofFIG. 12,

FIG. 12 is a fragmented simplified top plan of the alternative anchoringmeans of FIG. 11.

DETAILED DISCLOSURE FIGS. 1 and 2 A reservoir 10 has a peripherydefined'by inner faces of a surrounding containing wall 1.2, commonlycalled a berm, the berm having a generally horizontal upper surface 13serving "as a walkway. Sloping inner and outer surfaces 15 and 16 extenddownward from the walkway 13 at angles as shown. A floating coverassembly 18 according to the invention has aflexible impermeablediaphragm 20, an edge 22 of which defines in part a periphery of thediaphragm. The edge of the diaphragm is spaced outwards fromtheperiphery of the liquid so as to completely cover the liquid, thussubstantially reducing contamination of the liquid with precipitation orairborne particles.

A plurality of anchoring lines 24 of flexible tension links extendoutwards from the periphery of the diaphragm and across the berm, thelinks having inner and outer ends, the inner ends cooperating with edgesof the diaphragm and the outer ends cooperating with anchoring means,several embodiments of which are to be described. One embodiment of theanchoring means, a

ground anchor 26 is shown in FIG. 2. The links are tensioned resilientlyso as to apply an outwards force on the edges of the diaphragm tomaintain the diaphragm in a desired position relative to the reservoir,and to prevent edges of the diaphragm sinking below the surface.Resilient tensioning is used so as to limit tension in the cover bypermitting the diaphragm to move in response to a change in liquid levelfrom a predetermined high level to a predetermined low level as will beexplained.

A sump 28 is fltted at the lowest position of the diaphragm and drainsliquid collected on the diaphragm, drain means 30 (FIG. 2 only)extending from the sump to a sewer or other liquid disposal means. FIG.2 shows a simple gravity feed sump, in which a flexible pipe 32 connectsthe sump to a pipe 33 buried beneath the reservoir, the pipe 33 beingconnected to a sewer (not shown). More sumps can be fitted if necessary,the sumps having neutral bouyancy when empty so as to reduce load on thediaphragm. Water from the cover passes through a filtering screen toprevent oversize trash from entering the sump.

Material from which the diaphragm 20 is made is selected to withstandthe expected conditions of service, which in some areas can include lowtemperatures of perhaps minus 60F. to high temperatures of perhaps 120F. The cover should have sufficient tensile strength and flexibilitywithin the temperature range to resist relatively high local stressconcentrations, for instance around the sump and at the edges of thediaphragm. The material should be resistant to ultra-violetdeterioration, should be rot-andmildew-proof, and

should be opaque to sunlight to'inhibit algae growth. A

suitable material is a nylon-reinforced synthetic rubber such asHypalon, (registered trade mark of DuPont) two layers of Hypalon sheetsandwiching a woven nylon fabric. Thirty ounces per square yard ofmaterial has been found to be adequate, but weight of the material isdependent upon size of the diaphragm and expected load.

Throughout the specification the cover is shown for areservoircontaining water. Clearly, it can be used with reservoirscontaining other liquids, and material selected for the cover isdependent upon liquid to be protected. With some liquids a differenttype of material might be required. Nylon-reinforced Hypalon isparticularly adaptable to this application as it has an inherentelasticity which effectively augments the resilient tensioning of theanchoring lines, further reducing chances of accidental tearing of thediaphragm. Also, such material can be easily cleaned should it becomenecessary.

FIG. 3

The diaphragm I 42, the lower face being adapted to lie on an uppersurface 44 of the liquid. As the liquid level in the reservoir rises,periphery of the body of liquid increases and the edges of the diaphragmmove upwards and outwards due to the sloping inner surface 15. Thuseffective periphery of the diaphragm in a horizontal plane,i.e.,ignoring peripheral folds, increases to accommodate increase inperiphery of the body of liquid. Conversely, as the liquid level drops,the effective periphery of the diaphragm decreases, peripheral foldingincreasing.

The lower face 42 of the diaphragm contacts the liquid surface 44 at aposition 37, a portion of the diaphragm extending as an unsupported span38 from the edge 22 to the position 37. The span 38 is likely to bebetween about feet and feet and can vary beyond these limits, the spanbeing dependent on water level, loading on the diaphragm, and tensionand position of the anchoring lines.

The sump 28 has an alternative drain means 46 which includes a flexiblepipe 48 extending from the sump to a drain channel 50 on a side of theberm remote from the liquid. A pump (not shown) is provided either inthe sump 28, or in the drain channel 50 to pump a liq- 20 has upper andlower faces 41 and I uid from the sump to the channel. More than onepump can be provided in the sump, and the pumps can be set to operateautomatically, each pump being actuated automatically by a differentwater level in the sump.

The edge 22 of the diaphragm 20 is enclosed by a mantle 52, laterparticularized. One anchoring line 54 of the plurality of lines 24 hasinner and outer ends, the inner ends cooperating with the anchors, notshown. To reduce deterioration of the anchoring lines, the lines passthrough pipes under the walkway 13, the line 54 being shown passingthrough a pipe 55 buried in the berm.

FIG. 4 a

As previously stated the plurality of lines 24 are resiliently tensionedso as to accommodate changes in liquid level within the reservoir. Onemeans of resilient tensioning is to provide a resilient anchoring linein which an essentially inelastic link 61, such as a thin steel cable,is joined to an elastic link 63, such as a coil spring. The coil springhas sufficient extension under normal loads to accommodate the wholerange of liquid level within the reservoir, without exerting excessiveloads on the diaphragm. An alternative resilient line is made from asynthetic fibre rope, such as nylon, which in suitable lengths anddiameters has sufficient inherent resilience to accommodate liquid levelchanges.

The anchor 26 can be of the pole line hardware type, an expanding anchorsuch as stock No. C 64 as supplied by N. Slater Company Ltd., acorporation of Ontario, Canada, has been found to be suitable. A lengthof steel rope 67 extends from the anchor, which is joined at an outerend of the link 65, the steel rope 67 and anchor 26 serving as anchoringmeans.

A plurality of elongated stiffening members, two being shown anddesignated 69 and 70, are adjacent and cooperate with the periphery ofthe diaphragm. The stiffening members are disposed generallytangentially relative to edges of the diaphragm and have adjacent ends72 and 73 spaced when the liquid approaches a predetermined low level inthe reservoir. A plurality of tangential pockets, one pocket designated77, is spaced peripherally around the cover, each pocket accepting onestiffening member so as to distribute load applied to the stiffeningmembers along the periphery of the cover. The pocket 77 accepts themember 70, the outer ends 73 and 74 of which project beyond the pocketas shown. Ground bearing means, later particularized with reference toFIGS. 7 and 10, are secured to each outer end of the stiffening memberto support the stiffening member above the inner surface 15 of thecontaining walls. Resilient tensioning of anchoring line permits theground bearing means to move over the surface 15 permitting thediaphragm to follow changes in liquid level.

FIG. 5

An alternative means to resiliently tension the anchoring lines has ananchoring means which includes a tension distributing means 81 having ablock and tackle 82. An alternative anchoring line 83 has an inner endcoupled to the diaphragm and an outer end carrying a first sheave 85 ofthe block and tackle 82. The block and tackle has a sheave pair 87complementary to the first sheave and aligned with and spaced from thefirst sheave, the sheave pair being coupled by an anchor connector to arespective anchor 89 on a side of the second sheave remote from thefirst sheave. A coupling line 92 of a flexible tension line such asnylon rope has first and second ends, and extends from the first end,around one sheave of the sheave pair around the first sheave andreturning to the remaining sheave pair then extending to a second blockand tackle .96. A hand winch 94, serving as a line tensioning means,cooperates with the first endof the line, the winch having a lock so asto maintain tension in the line. The line 92 passes from the secondblock and tackle 96 to further block and tackles (not shown) distributedalong the berm. The second end of the line cooperates with an anchor(not shown), the anchor being spaced from the winch a distance whichdoes not exceed an optimum when considering energy losses assocaitedwith the line and block and tackles. When the coupling line 92 is beingtensioned, an operator operating the winch should pause frequently, lockthe winch so as to prevent unwinding, and, on a side remote from thewinch of each block and tackle apply a sideways force on the connectingline, i.e., at right angles to the line 92 as it extends to theadjacentblock and tackle. Such sideways pulling will tend to distribute tensionmore evenly along the coupling line to reduce excessive tension buildupin one portion of the line whilst a remaining portion of the lineexperiences relatively little tension.

Movement of the diaphragm from a high water level position to a lowwater level position results in a corresponding movement of the firstsheave 85 along the outer surface 16. The sheave 85 is thus spaced asuit able distance from an outer. end of the pipe 55 to accommodate suchmovement. Thecoupling line is a relatively light nylon rope, for exampleone-half inch diameter, and the anchoring lines are of a thicker rope,for example, three-quarter inch diameter. Such an arrangement providesan automatic safety feature in that the coupling line will break wellbefore the anchoring line, should excessive tension be experienced. Useof a relatively light nylon coupling line provides a resilienttensioning of the coupling line, which resilience is transmittedpartially to the anchoring lines to apply a resilient outwards force onthe periphery of the diaphragm. The block and tackles clearly multiplyforce in laterally from the upper sheave, the sheaves being spacedsufficiently from'the sloping surface 16 to permit rotation. A secondlower or anchor sheave 109 is similarly spaced below and laterally fromthe sheave 106, the sheaves 108 and 109 effectively straddling andspaced below from the sheaves 106. A further upper or diaphragm sheave110 is coupled to a similar anchoring line and is'part of a row ofspaced diaphragm sheaves extending along a portion of the containingwall adjacent the diaphragm, each sheave being coupled to a stiffeningmember. Further lower or anchor sheaves (not shown) similar to thesheaves 108 and 109 form a row of spaced anchor sheaves extending alonga portion of the containing wall adjacent anchors, the rows of upper andlower sheaves being staggered relative to each other.

A flexible tension link coupling line 111 having first and second endsextends from the first end, around the anchor sheave 109, across to theadjacent diaphragm sheave 106 and thence to the adjacent anchor sheave108, and thence successively to alternate sheaves in each row, the linedescribing a zig-zag along the outer surace 16 of the containing walltowards the second end of the line, which end cooperates with an anchor(not shown). A first end of the line cooperates with the line tensioningmeans 102 which includes a freely suspended weight 113 suspended from aframe 115. A block and tackle 116 couples the weight to the firstend ofthe line so that force from the weight 113 iseffectively multiplied toincrease tension applied to the line 111. The weight 113 is elevatedsufficiently to provide adequate travel to accommodate range of movementof the diaphragm 20. Thus tension in the coupling line is distributed tothe upper sheaves and maintains an outwards force on the diaphragm. Thecoupling line has less strength than the anchoring lines and diaphragmso that, in an excessive loading condition, the line 111 will breakfirst.

The coupling line 111 can also be tensioned with a hand winch similar tothe hand winch 94 of FIG. 5. Likewise the coupling line 92 of FIG. 5 canbe tensioned by a freely hanging weight similar to the weight 113 ofFIG. 6. With a freely hanging weight, movement of the weight provides aresilient tensioning independently of elasticity characteristics of thecoupling line. Thus if a hanging weight is used the coupling line can berelatively inelastic wire rope, thus reducing load losses in tensioning.However, if a wire rope coupling line is used, the coupling line shouldhave a lower tensile strength than the anchoring lline, or a weak linkshould be provided, so as to protect the anchoring lines and diaphragm.

. A further alternative (not shown) uses a plurality of hanging weights,each weight being coupled to a respective anchoring line. Each anchoringline passes over a pulley supported clear of the ground,the weight beingsecured to the outer end of the anchoring line. Tension in the line isthus transferred directly to the diaphragm, and, if sufficient weight isused the block and tackle can be eliminated. FIG. 7

The elongated stiffening member 69 is supported on ground bearing meansabove the inner face of the containing wall, theground bearing meanspermitting the periphery of the diaphragm to move relative to the wallto follow changes in liquid level. (One ground bearing means 121 securedto the outer end 72 is shown and includes a roller 123 journalled forrotation about an axis aligned with the elongated stiffening member. Thestiffening member 69 is cylindrical, suitably a tube, which passesthrough the pocket 77, the pocket being formed from a fold in thediaphragm, which pocket distributes load evenly along that portionof theperiphery defined by the pocket. The anchoring line 54 cooperates withthe outer end of the member 69' by means to be described with referenceto FIG. 8.

A support 125 extends from the end 69 and has an upper end having an eye(not shown), the eye accepting a peripheral line 127 (FIG. 8 only)threaded therethrough. The line 127 in combination with the support 125supports the mantle 52 clear of the roller 123 to prevent wear of themantle, which is made from a flexible sheet material, similar to butlighter than the sheet material used in the diaphragm. The mantle has aninner portion 129 extending from the line 127 to the diaphragm, and anouter portion 131) extending from the line 127 to the sloping innersurface 15. An inner edge 132 of the mantle is secured to the diaphragmadjacent the pocket, and an outer edge 134 is weighted to resistmovement of the outer portion. The weight can be a lengthof heavy pipein a pocket, or can be rocks or other ballast. The outer portion 130extends beyond a normal upper limit of travel of the edge 22 so as toprevent the roller from rolling over the outer edge 134. Sufficientslack is provided in the mantle to accommodate normal daily movements ofthe diaphragm, however with an excessive draw-down the outer edge isfree-to follow movement of the periphery inwards, thus maintaining thelower surface of the diaphragm in contact with the surface ofthe'liquid. Each stiffening member has an associated mantle, spacesbetween adjacent mantles providing clearance for the anchoring line 54.

- An alternative outer portion 135 is shown in broken outline andextends from the surface 13 of the berm and functions similarly. Toreduce wear of the anchoring line 24 as it passes through the ends ofthe pipe 55, a low friction, wear-reducing insert 137 is providedmanufactured from a tough plastic material, suitably nylon.

FIG. 8

As previously stated, adjacent outer ends 72 and 73 of the stiffeningmembers 69 and 70 are spaced sufficiently to permit movement of the endstowards each other as the diaphragm moves down the inner slope of thecontaining walls. The outer end 73 is supported on a roller 141 similarto'the roller 123 and a support 143 similar to the support 125 carriesthe peripheral line 127. A flexible tension link connector 145 extendsbetween the ends 72 and 73, midpoint of which connector is secured tothe anchoring line 54 as shown.v Pockets containing the stiffeningmembers 69 and 70 are spaced by a U-shaped cut-out 147 in the peripheryof the diaphragm 20.

The U-shaped cut-out is peripherally reinforced so that, when the liquidlevel approaches a predetermined high level and edges of the diaphragmare in a high position, there is sufficient strength or slackness in theU- shaped cut-out to essentially prevent tearing due to excessiveperipheral tension.'Common reinforcing means can be employed tostrengthen the U-shaped cut-out.

FIGS. 9 and An alternative ground bearing means for supportingaltemative stiffening members 151. and 152 eliminates the rollers 123and 124, the peripheral line 127, and the supports 125 and 143 of FIGS.7 and 8. Brackets 156 and; 157 extend from ends of the members 151 and152 and each bracket supports a castor, one such castor 158 being shownin FIG. 10. An alternative mantle 160, FIG. 10 only, has an inner edge162 secured to the diaphragm and an outer edge 164 weighted to reducemovement, similar to the outer edge 134 of FIG. 7. The castor 158extends below the bracket 156 and thus the mantle 160 is protected fromthe roller, thus the supports 125 and 143 and peripheral line 127 ofFIG. 8 are'not required. A flexible tension link connec- 'line 24,similarly to the connector of FIG. 8.

Commonly the sloping inner surface 15 of the containing wall is loosegravel and, particularly with a small diameter castor 158, a runway forthe castor is required to facilitate rolling along the inner surface.Such a runway can be a fabric-covered metal strip or other similarrelatively stiff surface which extends between upper and lower limits oftravel of the roller, and has a width sufficient to accommodatevariation in tracking of the ground bearing means. Ground bearing meansthat are journalled for rotation rotate about axes parallel to therespective stiffening member. Other types of ground bearing means, suchas skids, can be used to support the stiffening members.

OPERATION Irrespective of the type of anchoring line attachment,installation and operation of the diaphragm follows a similar procedure.The diaphragm is manufactured in one piece and transported to the sitein a rolled condition. Assuming a generally rectangular reservoir shownin FIG. 1, an outer edge of the rolled diaphragm is secured torespective anchoring lines and the diaphragm is unrolled from thesecured end. As portions of adjacent edges of the diaphragm areprogressively exposed, the portions are secured to respective anchoringlines until the diaphragm is completely unrolled and secured on all foursides. This securing is relatively loose and the position of thediaphragm relative to edges of the body of liquid can be adjusted byloosening anchoring lines on one side and tightening lines on oppositeside.

Under normal conditions the lower surface of portions of the diaphragmremote from the periphery is supported on the upper surface 44 (FIG. 2)of the liquid, limit of such support being the position 37 (FIG. 3). Atthe position 37 the diaphragm extends from the surface to the stiffeningmember which is supported on the sloping inner surface 15. Sufficientresilience in the anchoring lines is provided so that, when the liquidreaches a predetermined low level the position 37 is not more than abouttwenty feet from the containing wall. The diaphragm has sufficientstrength to support its own weight, plus some precipitation, for a shortunsupported span, but for a long unsupported span in which the diaphragmis not carried on the upper surface of the liquid, excessive diaphragmtension might be experienced unless a weak link is provided aspreviously described. At all time the sump is supported by the liquid,and should an excessive draw down of liquid below the predetermined lowlevel occur, tension in the diaphragm is limited by one or more of thecoupling lines or weak links breaking, thus relieving load on thediaphragm. As repair or replacement of a broken line is easy, this is arelatively fail-safe arrangement.

For routine maintenance the cover can be rolled back off the liquidsurface to be cleaned. An operator can work adjacent one edge of thediaphragm at a time, rolling the diaphragm back to expose the lowersurface thereof for cleaning.

FURTHER ALTERNATIVE FIGS. 11 and 12 In the following description,position of components of the anchoring means when the diaphragm is in ahigh position are shown in full line, and when the diaphragm is in a lowposition are shown in broken line.

An alternative anchoring means 170 cooperates with an edge 171 of thediaphragm 20, which diaphragm is supported on the surface 44 of theliquid shown in a high position. Alternative elongated stiffeningmembers 173 through 175 cooperate with the edge 171 and differ fromprevious stiffening members by being supported clear of the containingwall 12, that is ground bearing means ,of previously describedembodiments are not'provided'.

The anchoring means 170 has a post 178 extending upwards from thewalkway 13 adjacent the sloping surface 15. An elevated pulley 180 issupported clear of the walkway 13 by an arm 182 extending from an upperend of the post 178. An anchoring line 183 has an inner end connected tothe stiffening member 174 and an outer end carrying a weight 184 hangingfreely from the elevated pulley so as to tension the anchoring line. Asnatch block 186is secured relative to the containing wall by aconnecting line 187 which is coupled to a winch 188. The anchoring line183 passes from the stiffening member 174, under the snatch block 186and over the elevated pulley' 180 to the hanging weight, which, when thediaphragm is in the highest position, is clear of the ground. The pulley180 is sufficiently high so that, when the diaphragm moves to the lowposition (broken outline) the weight can move to an elevated position184.1 (broken outline) without interfering with the pulley.

An alternative mantle 191 has an inner edge 192 secured adjacent theperiphery of the diaphragm and an outer'edge 193 lying on the walkway13, space between the inner and outer edges defining width of themantle. The outer edge 193 is secured relative to the containing wall,preferably by a peripheral guy line (not shown) extending along the edgeand secured to the post 178 and an adjacent post 195, FIG. 12 only. Amantle bar 197, best seen in FIG. 12, is parallel to the stiffeningmember 174 and secured to and extending across the mantle at a positionabout midway between the inner and outeredges. The bar 197 defines aninner portion 198 of the mantle between the stiffening member and themantle bars, and an outer portion 199 between the mantle bar and theouter edge 193. Resilient mantle links 201 and 202 extend between theposts. 178 and 195 and the mantle bar 197 and have sufficient length andresilience to retain-the mantle bar adjacent the post when the diaphragmis in the high position. In the high position the inner portion 198 ofthe mantle is essentially taut and the outer portion 199 is slack,extending downwards from the mantle bar to the walkway. The innerportion is inclined so as to shed precipitation collected on the mantle,reducing chance of puddles forming on the mantle. The outer portion 199hangs downwards and is secured adjacent the ground at the outer edge193, effectively sealing edges of the diaphragm from wind which mightotherwise blow under the diaphragm.

When the water level approaches a low position, as shown in brokenoutline at 44.1, the edge of the diaphragm moves inwards to a lowposition, the stiffening member 174 assuming a low position 174.1, andthe snatch block 186 swinging to a low position 186.1. If necessary thewinch 188 can be loosened to increase length of the connecting lines187, thus reducing load on the. diaphragm. If required, the reel of thewinch can be spring-loaded so as to apply proportional to extension.

When the mantle is in the low position the mantle bar 197 is moved to alow position 197.1 by tension in the inner portion 198, which assumes alow position 198.1 (broken line), FIG. 11 extending from the stiffeningmember, and inclined so as to shed precipitation onto the diaphragm. Theresilient mantle links 201 and 202 extend towards the diaphragm,assuming stretched positions 201.1 and 202.1 the outer portion of themantle assuming an extended position 199.1 (broken outline) (FIG. 11)being taut and inclined so as to shed precipitation outwards from thediaphragm. As previously stated the weight 184 moves to elevatedposition 184.1, the anchoring line having sufficient length to accomaload on the line 187 modate movement of the periphery from the highposition of the diaphragm to the low position.

Thealternative anchoring means eliminates the pipes 55 (FIGS. 3 and 4)extending across the walkway, and as the ground bearing means areeliminated, there is no requirement for runways to support the groundbearing means. Operation of the means 170 follows closely that of thepreviously described embodiments. A major difference is that tension inthe anchoring lines is sufficient to suspend the stiffening membersclear of the containing wall to prevent abrasion. Also, because eachanchoring line is individually tensioned by a suspended weight,additional tension can be easily added where required to maintain thestiffening members clear of the wall.

We claim: I

1. A floating cover assembly for a body of liquid having a peripherydefined by inner surfaces of surrounding containing walls, the assemblyhaving:

a. a flexible impermeable diaphragm having upper and lower faces, and anedge defining a periphery thereof, the lower face being adapted to lieon the upper surface of the liquid, the'edge of the diaphragm being.spaced outwards from the periphery of the liquid, b. a plurality ofelongated stiffening members adjacent and cooperating with the peripheryof the diaphragm, the stiffening members having outer ends,

thereof, so as to drain liquid collected on theupper face of thediaphragm, the sump having drain means to drain the liquid collected, sothat the periphery of the diaphragm is anchored to the containing wallsand can move in response to a change in liquid level from apredetermined high level to a predetermined low level.

2. A floating cover assembly as claimed in claim 1 wherein thestiffening members are disposed generally tangentially relative to edgesof the diaphragm and cooperate with the edges of the diaphragm so thati. when the liquid level is somewhat above the predetermined low level,the edges of the diaphragm are in a low position and the ends of thestiffening members are spaced from ,ends of adjacent stiffening members,

ii. when the liquid level approaches the predetermined high level, theedges of the diaphragm are in a high position and have sufficient lengthto reduce a chance of tearing resulting from excessive peripheraltension in the diaphragm.

3. A floating cover assembly as claimed in claim 2 in which i. aplurality of tangential pockets are spaced peripherally around the edgesof the cover, the pockets accepting the stiffening members so as todistribute load applied to the stiffening members along the periphery ofthe cover.

4. A floating cover assembly as claimed in claim 3 in which i. the outerends of each stiffening member project beyond the respective pocket,

ii. ground bearing means are secured to each outer end of eachstiffening member to support the stiffening member above the inner facesof the containing walls,

so that when the liquid level changes, resilience in the tension linespermits the ground bearing means to move over the inner surface of thewall, permitting the diaphragm to follow changes in liquid level so asto maintain the lower face of the diaphragm generally in contact withthe surface of the liquid.

5. A floating cover assembly as. claimed in claim 4 in which the groundbearing means include:

i. rollers journalled for rotation about an axis parallel to therespective stiffening member.

6. A'floating cover assembly as claimed in claim 1 in which theanchoring means includes a tension distribution means having:

i. ablock and tackle having a first sheave coupled to the outer end ofthe anchoring line, and a sheave pair complementary to the first sheave,the sheave pair being coupled to a respective anchor on a side of thesheave pair remote from the first sheave,

ii. a flexible tension link coupling line having first and second ends,the line extending from the first end, around one sheave of the sheavepair, around the first sheave and returning to the remaining sheave ofthe sheave pair, thenextending to the second end,

iii. a line tensioning means cooperating with the first end of the line,

iv. an anchor cooperating with the second end of the line, so thattension in the coupling line is distributed to the first sheave andmaintains an outwards force on the diaphragm.

7. A floating cover assembly as claimed in claim 1 in which theanchoring means includes a tension distribution means having:

i. a row of spaced diaphragm sheaves journalled for iii. a flexibletension link coupling line having first and second ends, the lineextending from the first end, around a sheave of one row, across to anadjacentsheave in the other row, and thence successively to alternatesheaves ineach row, the coupling line describing a zig-zag along thesurface of the containing wall towards the second end of the line,

iv. a line tensioning means cooperating with the first end of the line,

v. an anchor cooperating with the second end of the line,

so that tension in the coupling line is distributed to the diaphragmsheaves and maintains an outward force on the diaphragm.

8. A floating cover assembly as claimed in claim 6 in which the linetensioning means includes:

i. a weight hanging freely from the first end of the line.

9. A floating cover assembly as claimed in claim 6 in which the linetensioning means includes:

i. a winch secured to the first end of the coupling line to applytension to the line, the winch having a lock so as to be locked inposition to maintain tension in the line.

10. A floating cover assembly as claimed in claim 1 in which i. a rolleris journalled for rotation at each outer end of each stiffening member,adjacent outer ends of adjacent stiffening members being spaced toprevent interference between adjacent rollers,

ii. a flexible tension link connector extends between the spacedadjacent outer ends of the adjacent stiffening members,

iii. a first sheave is coupled to the connector extending between theouter ends of the adjacent stiffening members,

iv. a sheave pair complementary to the first sheave is aligned with andspaced from the first sheave, the sheave pair being coupled to arespective anchor on a side of the sheave pair remote from the firstsheave,

v. a flexible tension link coupling line having first and second ends,the line extending from the first end, around one sheave of the sheavepair, around the first sheave and returning to the remaining sheavepair, thence extending to the second end,

vi. a line tensioning means cooperating with the first end of the line,

vii. an anchor cooperating with the second end of the line,

so the tension in the coupling line is transferred to the first sheaveand maintains an outwards force on the diaphragm.

11. A floating cover assembly as claimed in claim 1 further including:

f. a mantle having spaced inner and outer edges straddling thestiffening member, the inner edge being secured to the upper surface ofthe diaphragm inwards of the edge of the cover, the outer edge of themantle being spaced on a side of the stiffening member remote from theinner edge, spacing between the inner and outer edges providingsufficierit slack in the mantle to permit movement offt he stiffeningmember beneath the mantle, the outer""edge of'the mantle being supportedon and restricted against movement relative to the wherein the drainmeans includes:

i. a pipe extending from a sump to a position beyond the containingwall.

13. A floating cover assembly as claimed in claim 1 in which:

i. the anchoring line includes an elastic portion to provide resiliencefor securing the periphery of the diaphragm.

14. A floating cover assembly as claimed in claim 1 in which theanchoring means includes:

i. a pulley supported clear of the ground, one anchoring line passingover the pulley,

ii. a weight secured to the outer end of the anchoring line so that theweight hangs freely from the pulley, and applies a tension to theanchoring line, which tension is transferred to the edge of thediaphragm.

15. A floating cover assembly as claimed in claim 2 in which theanchoring means includes:

i. a snatch block secured relative to the containing wall,

ii. an elevated pulley supported clear of the ground; and the inner endsof the anchoring lines are coupled to the stiffening members, and theanchoring line passes under the snatch block and over the elevatedpulley to the outer end;

iii. a weight coupled to the outer end of the anchoring line, the weighthanging freely so as to tension the anchoring line, the anchoring linehaving sufficient length to accommodate movement of the periphery of thediaphragm from a low position to a high positlon.

16. A floating cover assembly as claimed in claim 15 further including:

i. a mantle having inner and outer edges defining a mantle width, theinner edge being secured adjacent periphery of the diaphragm, the outeredge being secured relative to the containing wall, mantle width beingsufficient to accommodate the diaphragm in low position,

ii. a mantle bar, parallel to the stiffening member and secured to andextending across the mantle at a position about midway between the innerand outer edges, the mantle bar together with the inner and outer edgesdefining inner and outer portions of the mantle respectively,

iii. resilient mantle links connecting the mantle bar with thecontaining wall,

so that when the diaphragm is in the high position the mantle bar isheld by the resilient mantle links so that the inner portion of themantle is essentially taut and l the outer portion is slack, and whenthe diaphragm is in the low position the inner and. outer portions areessentially taut and the resilient links are stretched.

1. A floating cover assembly for a body of liquid having a peripherydefined by inner surfaces of surrounding containing walls, the assemblyhaving: a. a flexible impermeable diaphragm having upper and lowerfaces, and an edge defining a periphery thereof, the lower face beingadapted to lie on the upper surface of the liquid, the edge of thediaphragm being spaced outwards from the periphery of the liquid, b. aplurality of elongated stiffening members adjacent and cooperating withthe periphery of the diaphragm, the stiffening members having outerends, c. anchoring means secured relative to the containing walls andspaced outwards from the periphery of the diaphragm, d. anchoring linesof flexible tension links extending outwards from the periphery of thediaphragm, the lines having inner and outer ends, the inner endscooperating with edges of the diaphragm, and the outer ends cooperatingwith the anchoring means, the lines being tensioned resiliently so as toapply an outwards force on the edge of the diaphragm, e. a sump fittedin the diaphragm at a lowest position thereof, so as to drain liquidcollected on the upper face of the diaphragm, the sump having drainmeans to drain the liquid collected, so that the periphery of thediaphragm is anchored to the containing walls and can move in responseto a change in liquid level from a predetermined high level to apredetermined low level.
 2. A floating cover assembly as claimed inclaim 1 wherein the stiffening members are disposed generallytangentially relative to edges of the diaphragm and cooperate with theedges of the diaphragm so that i. when the liquid level is somewhatabove the predetermined low level, the edges of the diaphragm are in alow position and the ends of the stiffening members are spaced from endsof adjacent stiffening members, ii. when the liquid level approaches thepredetermined high level, the edges of the diaphragm are in a highposition and have sufficient length to reduce a chance of tearingresulting from excessive peripheral tension in the diaphragm.
 3. Afloating cover assembly as claimed in claim 2 in which i. a plurality oftangential pockets are spaced peripherally around the edges of thecover, the pockets accepting the stiffening members so as to distributeload applied to the stiffening members along the periphery of the cover.4. A floating cover assembly as claimed in claim 3 in which i. the outerends of each stiffening member project beyond the respective pocket, ii.ground bearing means are secured to each outer end of each stiffeningmember to support the stiffening member above the inner faces of thecontaining walls, so that when the liquid level changes, resilience inthe tension lines permits the ground bearing means to move over theinner surface of the wall, permitting the diaphragm to follow changes inliquid level so as to maintain the lower face of the diaphragm generallyin contact with the surface oF the liquid.
 5. A floating cover assemblyas claimed in claim 4 in which the ground bearing means include: i.rollers journalled for rotation about an axis parallel to the respectivestiffening member.
 6. A floating cover assembly as claimed in claim 1 inwhich the anchoring means includes a tension distribution means having:i. a block and tackle having a first sheave coupled to the outer end ofthe anchoring line, and a sheave pair complementary to the first sheave,the sheave pair being coupled to a respective anchor on a side of thesheave pair remote from the first sheave, ii. a flexible tension linkcoupling line having first and second ends, the line extending from thefirst end, around one sheave of the sheave pair, around the first sheaveand returning to the remaining sheave of the sheave pair, then extendingto the second end, iii. a line tensioning means cooperating with thefirst end of the line, iv. an anchor cooperating with the second end ofthe line, so that tension in the coupling line is distributed to thefirst sheave and maintains an outwards force on the diaphragm.
 7. Afloating cover assembly as claimed in claim 1 in which the anchoringmeans includes a tension distribution means having: i. a row of spaceddiaphragm sheaves journalled for rotation and extending along a portionof the containing wall adjacent the diaphragm, each sheave being coupledto a stiffening member, ii. a row of spaced anchor sheaves journalledfor rotation, the anchor sheaves being spaced along a portion of thecontaining wall adjacent anchors, each sheave being coupled to ananchor, the rows of sheaves being staggered relative to each other, iii.a flexible tension link coupling line having first and second ends, theline extending from the first end, around a sheave of one row, across toan adjacent sheave in the other row, and thence successively toalternate sheaves in each row, the coupling line describing a zig-zagalong the surface of the containing wall towards the second end of theline, iv. a line tensioning means cooperating with the first end of theline, v. an anchor cooperating with the second end of the line, so thattension in the coupling line is distributed to the diaphragm sheaves andmaintains an outward force on the diaphragm.
 8. A floating coverassembly as claimed in claim 6 in which the line tensioning meansincludes: i. a weight hanging freely from the first end of the line. 9.A floating cover assembly as claimed in claim 6 in which the linetensioning means includes: i. a winch secured to the first end of thecoupling line to apply tension to the line, the winch having a lock soas to be locked in position to maintain tension in the line.
 10. Afloating cover assembly as claimed in claim 1 in which i. a roller isjournalled for rotation at each outer end of each stiffening member,adjacent outer ends of adjacent stiffening members being spaced toprevent interference between adjacent rollers, ii. a flexible tensionlink connector extends between the spaced adjacent outer ends of theadjacent stiffening members, iii. a first sheave is coupled to theconnector extending between the outer ends of the adjacent stiffeningmembers, iv. a sheave pair complementary to the first sheave is alignedwith and spaced from the first sheave, the sheave pair being coupled toa respective anchor on a side of the sheave pair remote from the firstsheave, v. a flexible tension link coupling line having first and secondends, the line extending from the first end, around one sheave of thesheave pair, around the first sheave and returning to the remainingsheave pair, thence extending to the second end, vi. a line tensioningmeans cooperating with the first end of the line, vii. an anchorcooperating with the second end of the line, so the tension in thecoupling line is transferred to the first sheave and maintains anoutwards force on the diaphragm.
 11. A floating cover assembly asclaimed in claim 1 further including: f. a mantle having spaced innerand outer edges straddling the stiffening member, the inner edge beingsecured to the upper surface of the diaphragm inwards of the edge of thecover, the outer edge of the mantle being spaced on a side of thestiffening member remote from the inner edge, spacing between the innerand outer edges providing sufficient slack in the mantle to permitmovement of the stiffening member beneath the mantle, the outer edge ofthe mantle being supported on and restricted against movement relativeto the containing wall, the mantle having clearance for the anchoringline to extend therethrough.
 12. A floating cover assembly as claimed inclaim 1 wherein the drain means includes: i. a pipe extending from asump to a position beyond the containing wall.
 13. A floating coverassembly as claimed in claim 1 in which: i. the anchoring line includesan elastic portion to provide resilience for securing the periphery ofthe diaphragm.
 14. A floating cover assembly as claimed in claim 1 inwhich the anchoring means includes: i. a pulley supported clear of theground, one anchoring line passing over the pulley, ii. a weight securedto the outer end of the anchoring line so that the weight hangs freelyfrom the pulley, and applies a tension to the anchoring line, whichtension is transferred to the edge of the diaphragm.
 15. A floatingcover assembly as claimed in claim 2 in which the anchoring meansincludes: i. a snatch block secured relative to the containing wall, ii.an elevated pulley supported clear of the ground; and the inner ends ofthe anchoring lines are coupled to the stiffening members, and theanchoring line passes under the snatch block and over the elevatedpulley to the outer end; iii. a weight coupled to the outer end of theanchoring line, the weight hanging freely so as to tension the anchoringline, the anchoring line having sufficient length to accommodatemovement of the periphery of the diaphragm from a low position to a highposition.
 16. A floating cover assembly as claimed in claim 15 furtherincluding: i. a mantle having inner and outer edges defining a mantlewidth, the inner edge being secured adjacent periphery of the diaphragm,the outer edge being secured relative to the containing wall, mantlewidth being sufficient to accommodate the diaphragm in low position, ii.a mantle bar, parallel to the stiffening member and secured to andextending across the mantle at a position about mid-way between theinner and outer edges, the mantle bar together with the inner and outeredges defining inner and outer portions of the mantle respectively, iii.resilient mantle links connecting the mantle bar with the containingwall, so that when the diaphragm is in the high position the mantle baris held by the resilient mantle links so that the inner portion of themantle is essentially taut and the outer portion is slack, and when thediaphragm is in the low position the inner and outer portions areessentially taut and the resilient links are stretched.